1. Field of the Invention
This invention relates to the distribution of powder products and relates more particularly to the coating of glass with a layer of metal oxides obtained by pyrolysis of a powder of organometallic compounds sprayed on the glass at high temperature.
2. Description of the Prior Art
When glass is to be coated with a layer of oxides such as the oxides of Fe, Cr, Co, Ti, Al, Sn or Cu, for reflecting solar heat radiation, tinting, or increasing the hardness of the glass articles, dishes, or bottles, for example, the glass is often sprayed with a solution containing organometallic compounds that can be transformed into metal oxides at high temperature.
However, this process exhibits drawbacks. In particular it produces layers with irregular metal oxides and, moreover, cools the glass too much. This is particularly bothersome for thin glass which can be broken. Such a process also requires the use of solvents that may be harmful, or which are flammable or which are expensive.
To avoid these drawbacks, attempts have been made to spray the glass directly with powdered metal rather than with a solvent containing the metal compounds.
In the attempt to achieve a homogeneous distribution of the sprayed powder over the entire surface of the glass, it is known from Patent EP 6064 that the powder may be distributed on the glass with a device comprising a distribution slot placed over the entire wide width of the glass strip passing under it, with the slot being preceded by a primary slot which is fed powder by a multiplicity of pipes.
The process and device of EP 6064 have made it possible to avoid some of the drawbacks associated with the spraying of a solution and have improved the quality of the coated products so manufactured. However, when it is desired to increase the treatment width, for example, when it is desired to coat glass ribbons 4 m wide, or when it is desired to reduce the delivery of carrier gas to cool the glass less to obtain a still higher pyrolysis efficiency, or when it is desired to obtain even thinner and more homogeneous coatings, new difficulties are encountered. For example, the powder of the organometallic compounds adheres to the walls of the pipes that are carrying it and accumulates on the pipe walls. This can result in altering the delivery of powder and therefore the quality of the coating.
Further, only a relatively slight resistance of the deposited metal oxide layers to chemical agents can be noted, perhaps due to the high traveling speed of the substrates to be coated under the powder distribution slot.
Therefore, a need continues to exist for a process which distributes powders in regular, homogeneous coatings having uniform thickness, which are resistant to chemical attack, such that the devices employed to distribute the powders do not become clogged with the powders as the powders are distributed.